Fix version of proper

```
$ make test
==> hamcrest-erlang (compile)
==> hamcrest-erlang (post_compile)
==> hamcrest-erlang (xref)
==> hamcrest-erlang (get-deps)
ERROR: Dependency dir /Users/yuki_ito/dev/erlang/hamcrest-erlang/deps/proper failed application validation with reason:
{version_mismatch,{"/Users/yuki_ito/dev/erlang/hamcrest-erlang/deps/proper/src/proper.app.src",
                   {expected,"1.0"},
                   {has,"1.1"}}}.
ERROR: 'get-deps' failed while processing /Users/yuki_ito/dev/erlang/hamcrest-erlang: rebar_abort
make: *** [test] Error 1
```